1. FIELD OF THE INVENTION
This invention relates to continuous coal mining machines and more particularly to an improved rotary cutting head which permits an increase in production while decreasing respiral dust formed during the cutting process.
2. DESCRIPTION OF THE PRIOR ART
Many different methods have been employed in the mining of coal and in the past fifty years the development of mechanization in the mining of coal has virtually eliminated manual mining techniques. A large increase in productivity has been obtained by the design and development of the rotary head continuous mining machines which use a multiplicity of bits fixed to a rotating drum which may be advanced into the coal face and moved up or down to fragment the face of the coal seam or formation. With over 2,000 of these machines now in use and accounting for approximately one-half of the production of coal from underground coal mines, the employment of these machines has increased the problem of primary dust generation of the faces during cutting by rotation of the cutting teeth or tools. During the fragmentation process at the face of the coal deposit, which is responsible for the production of both airborne and non-airborne dust, dust generation is determined by such machine parameters as bit type, bit angle, spacing between bits, depth of cut and rotational speed. Research by the Bureau of Mines has involved an analysis of the effect of rotary cutting heads on a continuous mining machine and a determination of where and how primary dust is produced at the face. As result of that analysis, it has become apparent that where a pick or tool bit enters the coal face at zero depth due to its epitroichoidal path, the machine has an inherent potential for high dust production with an associated high energy demand. Thus, presently employed rotary head continuous mining machines are inherent dust producers. It has been determined that the limiting factor to dust reduction is the circular path with continuous entry and exit of each pick or bit in the face.
It is accordingly an object of the present invention to provide a new linear cutting rotary head for a continuous mining machine which will cut at a constant depth.
A further problem in the use of conventional rotary head continuous mining machines is that the constantly changing depth of a bit following an epitrichoidal path does not permit an optimum spacing for the cutting bits. Since deep cutting of coal with rotary machines appears to be the solution to dust generation during cutting, this presents the problem of using fewer bits with wide spacing to accommodate the deeper cutting most effectively which then produces coring at shallow cuts since there are too few bits for shallow cutting. Indeed, this is a paradox because one should cut deep to avoid dust but one increases the amount of dust by coring during deep cuts because there are too few bits. It is obvious, therefore, that the presently designed rotary head machines are therefore not amendable to dust reduction with high productivity due to their inherent design faults. It is apparent, therefore, that an ideal cutting machine would comprise a rotary head for high productivity using only deep linear cuts to reduce dust generation to a minimum while maintaining optimum bit spacing.
It is, therefore, a further object of this invention to provide an improved rotary head continuous mining machine which optimizes these three parameters.
It is a further object of this invention to provide an improved continuous mining machine which may be modified by the substitution of a new rotary cutting head which provides full linear shear and sump cuts without the necessity of modifying all other existing parts including those needed for propulsion, trackage electric and/or hydraulic motors to the power track, existing boom with vertical and/or horizontal movement and the existing means of collecting cut coal and conveying it to an appropriate shuttle car or belt transport system.